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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="pseudo-ops"></a>Pseudo P-CODE Operations</h2></div></div></div>
<p>
Practical analysis systems need to be able to describe operations, whose exact effect on a machine's
memory state is not fully modeled. P-code allows for this by defining a small set of
<span class="emphasis"><em>pseudo</em></span> operators. Such an operator is generally treated as a placeholder
for some, possibly large, sequence of changes to the machine state. In terms of analysis,
either the operator is just carried through as a black-box or it serves as a plug-in point for operator
substitution or other specially tailored transformation. Pseudo operators may violate the requirement
placed on other p-code operations that all effects must be explicit.
</p>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="cpui_userdefined"></a>USERDEFINED</h3></div></div></div>
<div class="informalexample"><div class="table">
<a name="userdefined.htmltable"></a><table xml:id="userdefined.htmltable" frame="above" width="80%" rules="groups">
<col width="23%">
<col width="15%">
<col width="61%">
<thead><tr>
  <td align="center" colspan="2"><span class="bold"><strong>Parameters</strong></span></td>
  <td><span class="bold"><strong>Description</strong></span></td>
</tr></thead>
<tbody>
<tr>
  <td align="right">input0</td>
  <td>(<span class="bold"><strong>special</strong></span>)</td>
  <td>Constant ID of user-defined op to perform.</td>
</tr>
<tr>
  <td align="right">input1</td>
  <td></td>
  <td>First parameter of user-defined op.</td>
</tr>
<tr>
  <td align="right">...</td>
  <td></td>
  <td>Additional parameters of user-defined op.</td>
</tr>
<tr>
  <td align="right">[output]</td>
  <td></td>
  <td>Optional output of user-defined op.</td>
</tr>
</tbody>
<tfoot>
<tr>
  <td align="center" colspan="2"><span class="bold"><strong>Semantic statement</strong></span></td>
  <td></td>
</tr>
<tr>
  <td></td>
  <td colspan="2"><code class="code">userop(input1, ... );</code></td>
</tr>
<tr>
  <td></td>
  <td colspan="2"><code class="code">output = userop(input1,...);</code></td>
</tr>
</tfoot>
</table>
</div></div>
<p>
This is a placeholder for (a family of) user-definable p-code
instructions. It allows p-code instructions to be defined with
semantic actions that are not fully specified. Machine instructions
that are too complicated or too esoteric to fully implement can use
one or more <span class="bold"><strong>USERDEFINED</strong></span> instructions
as placeholders for their semantics.
</p>
<p>
The first input parameter input0 is a constant ID assigned by the specification
to a particular semantic action. Depending on how the specification
defines the action associated with the ID,
the <span class="bold"><strong>USERDEFINED</strong></span> instruction can take
an arbitrary number of input parameters and optionally have an output
parameter. Exact details are processor and specification dependent.
Ideally, the output parameter is determined by the input
parameters, and no variable is affected except the output
parameter. But this is no longer a strict requirement, side-effects are possible.
Analysis should generally treat these instructions as a “black-box” which
still have normal data-flow and can be manipulated symbolically.
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="cpui_cpoolref"></a>CPOOLREF</h3></div></div></div>
<div class="informalexample"><div class="table">
<a name="cpoolref.htmltable"></a><table xml:id="cpoolref.htmltable" frame="above" width="80%" rules="groups">
<col width="23%">
<col width="15%">
<col width="61%">
<thead><tr>
  <td align="center" colspan="2"><span class="bold"><strong>Parameters</strong></span></td>
  <td><span class="bold"><strong>Description</strong></span></td>
</tr></thead>
<tbody>
<tr>
  <td align="right">input0</td>
  <td></td>
  <td>Varnode containing pointer offset to object.</td>
</tr>
<tr>
  <td align="right">input1</td>
  <td>(<span class="bold"><strong>special</strong></span>)</td>
  <td>Constant ID indicating type of value to return.</td>
</tr>
<tr>
  <td align="right">...</td>
  <td></td>
  <td>Additional parameters describing value to return.</td>
</tr>
<tr>
  <td align="right">output</td>
  <td></td>
  <td>Varnode to contain requested size, offset, or address.</td>
</tr>
</tbody>
<tfoot>
<tr>
  <td align="center" colspan="2"><span class="bold"><strong>Semantic statement</strong></span></td>
  <td></td>
</tr>
<tr>
  <td></td>
  <td colspan="2"><code class="code">output = cpool(input0,intput1);</code></td>
</tr>
</tfoot>
</table>
</div></div>
<p>
This operator returns specific run-time dependent values from the
<span class="emphasis"><em>constant pool</em></span>.  This is a concept for object-oriented
instruction sets and other managed code environments, where some details about
how instructions behave can be deferred
until run-time and are not directly encoded in the instruction. 
The <span class="bold"><strong>CPOOLREF</strong></span> operator acts a query to the system to
recover this type of information. The first parameter is a
pointer to a specific object, and subsequent parameters are IDs or other special constants
describing exactly what value is requested, relative to the object. The canonical example
is requesting a method address given just an ID describing the method and a specific object, but
<span class="bold"><strong>CPOOLREF</strong></span> can be used as a placeholder for recovering
any important value the system knows about. Details about this instruction, in terms
of emulation and analysis, are necessarily architecture dependent.
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="cpui_new"></a>NEW</h3></div></div></div>
<div class="informalexample"><div class="table">
<a name="new.htmltable"></a><table xml:id="new.htmltable" frame="above" width="80%" rules="groups">
<col width="23%">
<col width="15%">
<col width="61%">
<thead><tr>
  <td align="center" colspan="2"><span class="bold"><strong>Parameters</strong></span></td>
  <td><span class="bold"><strong>Description</strong></span></td>
</tr></thead>
<tbody>
<tr>
  <td align="right">input0</td>
  <td></td>
  <td>Varnode containing class reference</td>
</tr>
<tr>
  <td align="right">[input1]</td>
  <td></td>
  <td>If present, varnode containing count of objects to allocate.</td>
</tr>
<tr>
  <td align="right">output</td>
  <td></td>
  <td>Varnode to contain pointer to allocated memory.</td>
</tr>
</tbody>
<tfoot>
<tr>
  <td align="center" colspan="2"><span class="bold"><strong>Semantic statement</strong></span></td>
  <td></td>
</tr>
<tr>
  <td></td>
  <td colspan="2"><code class="code">output = new(input0);</code></td>
</tr>
</tfoot>
</table>
</div></div>
<p>
This operator allocates memory for an object described by the first parameter and
returns a pointer to that memory.
This is used to model object-oriented instruction sets where object allocation is an atomic operation.
Exact details about how memory is affected by a <span class="bold"><strong>NEW</strong></span> operation is generally
not modeled in these cases, so the operator serves as a placeholder to allow analysis to proceed.
</p>
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